Cold-active β-galactosidase from Weissella confusa SW1 for the preparation of low-lactose milk

Abstract

β-Galactosidases can be used to degrade lactose in milk to prepare lactose-free milk, which is sweeter than ordinary milk and suitable for people with lactose intolerance. The β-galactosidase gene (WcGal2809) was cloned from Weissella confusa SW1 and successfully expressed in Escherichia coli BL21(DE3). The active WcGal2809 was identified to be a heterodimer composed of two distinct proteins LacL (72.4 kDa) and LacM (33.2 kDa), and it belonged to glycoside hydrolase family 2. The purified WcGal2809 showed the maximum activity at 25 °C and pH 7.0 for o-nitrophenyl-β-D-galactopyranoside (oNPG). WcGal2809 was strongly activated by Mn²⁺, Mg²⁺, and Fe²⁺, and significantly inhibited by Zn²⁺, Cu²⁺, and Ni⁺. The activity of WcGal2809 decreased quickly after incubation at 40 °C or higher temperature, suggesting it was a cold-adapted enzyme. Additionally, 6 U of WcGal2809 could hydrolyze 85.23 % of the lactose in 1 mL of milk at 25 °C after incubation for 48 h, while 2 U of WcGal2809 could hydrolyze 74.40 % of the lactose in 1 mL of milk at 25 °C after incubation for 7 d. Taken together, WcGal2809 is a promising industrial biocatalyst for efficiently hydrolyzing lactose in milk at room temperature during milk storage or transportation.